1. Field of the Invention
This invention relates to a process for producing a water-soluble alkyd resin using a 1,2-epoxyalkane or straight-chain internal epoxyalkane. This alkyd resin forms a cured product having superior resistance to yellowing and superior gloss as well as superior hardness and marked flexibility.
2. Description of the Prior Art
Water-soluble alkyd resins are obtained usually by treating oil-soluble resins to render them water-soluble. As is well known, oil and fat-modified water-soluble alkyd resins contain a fatty acid ester at a side chain and are obtained by reacting dicarboxylic acids such as phthalic anhydride, polyhydric alcohols such as glycerol and fatty acids or fatty acid glycerides. These types of alkyd resins are described in Journal of Paint Technology, Vol. 40, No. 525, pages 450 to 458 (October, 1968) and have been used extensively as resins for paints.
Baked coatings of paints obtained by using these oil and fat-modified alkyd resins as raw materials have excellent properties, but have the defect that they yellow markedly and have poor weatherability.
One known water-soluble alkyd resin prepared by using a 1,2-epoxyalkane is a reaction product of 1,2-octene oxide, phthalic anhydride and dipentaerythritol (e.g., as described in British Pat. No. 1,298,773). This alkyd resin is prepared by the ring-opening esterification of phthalic anhydride with dipentaerythritol and then the ring-opening esterification reaction of 1,2-octene oxide with the resulting product. Baked coatings from this resin are hard and brittle and this resin lacks compatibility with other resins. Hence, this resin is not entirely satisfactory as a resin for paints.